/*
 * Copyright (C) 2007 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.io;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.List;

/**
 * Provides utility methods for working with resources in the classpath. Note
 * that even those these methods use {@link URL} parameters, they are usually
 * not appropriate for HTTP or other non-classpath resources.
 * 
 * <p>
 * All method parameters must be non-null unless documented otherwise.
 * 
 * @author Chris Nokleberg
 * @author Ben Yu
 * @since 2009.09.15 <b>tentative</b>
 */
public final class Resources {

    /**
     * Returns a factory that will supply instances of {@link InputStream} that
     * read from the given URL.
     * 
     * @param url
     *            the URL to read from
     * @return the factory
     */
    public static InputSupplier<InputStream> newInputStreamSupplier(
            final URL url) {
        checkNotNull(url);
        return new InputSupplier<InputStream>() {
            public InputStream getInput() throws IOException {
                return url.openStream();
            }
        };
    }

    /**
     * Returns a factory that will supply instances of {@link InputStreamReader}
     * that read a URL using the given character set.
     * 
     * @param url
     *            the URL to read from
     * @param charset
     *            the character set used when reading the URL contents
     * @return the factory
     */
    public static InputSupplier<InputStreamReader> newReaderSupplier(URL url,
            Charset charset) {
        return CharStreams.newReaderSupplier(newInputStreamSupplier(url),
                charset);
    }

    /**
     * Reads all bytes from a URL into a byte array.
     * 
     * @param url
     *            the URL to read from
     * @return a byte array containing all the bytes from the URL
     * @throws IOException
     *             if an I/O error occurs
     */
    public static byte[] toByteArray(URL url) throws IOException {
        return ByteStreams.toByteArray(newInputStreamSupplier(url));
    }

    /**
     * Reads all characters from a URL into a {@link String}, using the given
     * character set.
     * 
     * @param url
     *            the URL to read from
     * @param charset
     *            the character set used when reading the URL
     * @return a string containing all the characters from the URL
     * @throws IOException
     *             if an I/O error occurs.
     */
    public static String toString(URL url, Charset charset) throws IOException {
        return CharStreams.toString(newReaderSupplier(url, charset));
    }

    /**
     * Streams lines from a URL, stopping when our callback returns false, or we
     * have read all of the lines.
     * 
     * @param url
     *            the URL to read from
     * @param charset
     *            the character set used when reading the URL
     * @param callback
     *            the LineProcessor to use to handle the lines
     * @return the output of processing the lines
     * @throws IOException
     *             if an I/O error occurs
     */
    public static <T> T readLines(URL url, Charset charset,
            LineProcessor<T> callback) throws IOException {
        return CharStreams.readLines(newReaderSupplier(url, charset), callback);
    }

    /**
     * Reads all of the lines from a URL. The lines do not include
     * line-termination characters, but do include other leading and trailing
     * whitespace.
     * 
     * @param url
     *            the URL to read from
     * @param charset
     *            the character set used when writing the file
     * @return a mutable {@link List} containing all the lines
     * @throws IOException
     *             if an I/O error occurs
     */
    public static List<String> readLines(URL url, Charset charset)
            throws IOException {
        return CharStreams.readLines(newReaderSupplier(url, charset));
    }

    /**
     * Copies all bytes from a URL to an output stream.
     * 
     * @param from
     *            the URL to read from
     * @param to
     *            the output stream
     * @throws IOException
     *             if an I/O error occurs
     */
    public static void copy(URL from, OutputStream to) throws IOException {
        ByteStreams.copy(newInputStreamSupplier(from), to);
    }

    /**
     * Returns a {@code URL} pointing to {@code resourceName} if the resource is
     * found in the class path. {@code Resources.class.getClassLoader()} is used
     * to locate the resource.
     * 
     * @throws IllegalArgumentException
     *             if resource is not found
     */
    public static URL getResource(String resourceName) {
        URL url = Resources.class.getClassLoader().getResource(resourceName);
        checkArgument(url != null, "resource %s not found.", resourceName);
        return url;
    }

    /**
     * Returns a {@code URL} pointing to {@code resourceName} that is relative
     * to {@code contextClass}, if the resource is found in the class path.
     * 
     * @throws IllegalArgumentException
     *             if resource is not found
     */
    public static URL getResource(Class<?> contextClass, String resourceName) {
        URL url = contextClass.getResource(resourceName);
        checkArgument(url != null, "resource %s relative to %s not found.",
                resourceName, contextClass.getName());
        return url;
    }
}
